1. Field of the Invention
The present invention relates to a method for managing corrosion of an underground structure, and in particular, it relates to a method for installing an anode to protect an underground metal pipeline.
2. Background Art
Corrosion, and in particular corrosion of metal structures, is a problem that must regularly be addressed in a wide variety of areas. For example, in the automotive industry, metal parts are often plated or coated to protect them from road salt and moisture in hopes of increasing their longevity. Indeed, many traditionally metal parts are currently being replaced with polymeric components, which are not only lighter and perhaps more cost effective to produce, but are generally impervious to electrochemical corrosion often experienced by metals.
Other industries have also employed non-metal structures, or at least coated metal structures. For example, new installations of natural gas delivery systems may include wrapped steel gas pipelines to help inhibit corrosion. These coated steel pipelines generally have a much longer expected life span than their bare steel counterparts; however, the coating on the wrapped steel pipelines will eventually degrade. Moreover, many hundreds or thousands of miles of pipeline were installed before wrapped steel pipe was readily available. Therefore, corrosion of existing pipeline structures—and eventually, corrosion of recently-laid wrapped pipeline structures—present an ongoing challenge for those working in the gas industry.
One way in which this problem has been addressed is through the use of cathodic protection for the steel pipelines. In its simplest form, cathodic protection includes the use of a galvanic couple—i.e., the metal to be protected is electrically connected to another metal that is more anodic than the metal to be protected. The anode becomes sacrificial, giving up electrons in an oxidation reaction. In this situation, the metal to be protected becomes a cathode, experiencing a reduction reaction which protects the metal.
In the case of an underground steel pipeline, it has been common practice to bury an anode rod in proximity to the pipeline, and connect the rod and the pipeline together with an electrical conductor, such as a copper wire. Because these pipelines may remain in the ground for decades, and because the anode can, over time, experience significant deterioration, it is important to be able to determine if a particular anode remains an effective corrosion inhibitor for the pipeline. One way this is accomplished is by terminating the connection between the anode and the pipeline in a test box, sometimes called a “curb box”. The test box is usually located near the surface of the ground, and has a top cover which can be removed to provide access to the interior of the box. In the box, a wire leading from the pipeline is attached to a wire leading from the anode. By placing a volt meter in between these wires and measuring the voltage potential, the relative effectiveness of the anode can be determined. When it is determined that an anode has deteriorated beyond the point at which it continues to be effective to inhibit corrosion of the steel pipeline, a new anode is required.
In practice, the existing anode may be allowed to remain, while a second anode is installed. Although the electrical connection to the pipeline is made inside the test box, installing the anode in the ground can be very expensive, time consuming, and disruptive. One particularly onerous aspect of installing a new anode to protect an underground pipeline is the cost of the relatively large excavation project that is used to place the new anode in the ground near the test box. Test boxes are sometimes located in sidewalks, or along the edges of busy thoroughfares. In cases such as these, it is common for a municipality to require the purchase of a permit to break through the concrete or asphalt surrounding the test box. In addition to the purchase price of the permit, it may be necessary for the construction company to post a bond. Drawings of the proposed excavation and placement of the anode may need to be submitted, and additional fees are often required.
The administrative costs for such a project in a large city, for example New York City, may total a thousand dollars or more. For a large utility, which may place hundreds of anodes along miles of pipeline each year, these costs represent a huge expense. In addition, there is the equipment required for the excavation project itself, which may include a jack hammer, or other impact device, and a backhoe, or other removal equipment, needed to dig the hole and remove the debris after the concrete or asphalt surface is penetrated. Such a project is not only expensive and time consuming for the company performing it, but is also disruptive to the public. A typical excavation to place an anode is loud, time consuming, and may cause traffic—pedestrian and/or vehicle traffic—to be rerouted, not only while the anode is being installed, but afterward during the time the newly-poured replacement concrete or asphalt sets-up.
Therefore, a need exists for a method for managing corrosion of an underground structure, and in particular a method for installing an anode for a steel pipeline that does not require destruction of a paved surface surrounding a test box, with all of its attendant costs and disruptions.